Vibration sensor and sensor module

ABSTRACT

A vibration sensor according to an embodiment includes a laminated body. The laminated body includes a support layer a first end of which is fixed; a piezoelectric layer on the support layer; an insulating layer disposed between the support layer and the piezoelectric layer; a common electrode disposed on a first principal surface of the piezoelectric layer; a first sensing electrode disposed in a first area on a second principal surface of the piezoelectric layer on the side opposite to the first principal surface; and a drive electrode disposed in a second area different from the first area on the second principal surface of the piezoelectric layer. The first area is located near the first end of the support layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 16/286,708,filed Feb. 27, 2019, which is based upon and claims the benefit ofpriority from Japanese Patent Application No. 2018-100554, filed on May25, 2018; the entire contents of which are incorporated herein byreference.

FIELD

Embodiments described herein relate generally to vibration sensors and asensor module.

BACKGROUND

Vibration sensors have conventionally been around as sensors to detectminute vibrations of structures, electronic devices, or the like, andgrasp the status and state thereof. Vibration sensors are very importantin securing safety and reliability of structures, electronic devices, orthe like, and in determining whether maintenance needs to be performed,for example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram illustrating an example structure of avibration sensor according to a first embodiment;

FIG. 1B is a schematic diagram illustrating an example structure of avibration sensor according to a first embodiment;

FIG. 2 is a diagram for illustrating the vibration sensor used for astudy to determine the size of a sensing electrode according to thefirst embodiment;

FIG. 3 is a graph illustrating sensitivity characteristics with respectto the contraction ratio of the electrode in the length direction of thevibration sensor according to the first embodiment;

FIG. 4 is a graph illustrating sensitivity characteristics with respectto the contraction ratio of the electrode in the width direction of thevibration sensor according to the first embodiment;

FIG. 5A is a schematic diagram illustrating an example structure of avibration sensor according to a second embodiment;

FIG. 5B is a schematic diagram illustrating an example structure of avibration sensor according to a second embodiment;

FIG. 6 is a schematic diagram illustrating an example structure of avibration sensor according to a third embodiment;

FIG. 7 is a diagram illustrating an example of an electric connection ofa sensor portion in the vibration sensor illustrated in FIG. 6 ;

FIG. 8 is a diagram illustrating an example of an electric connection ofa drive portion in the vibration sensor illustrated in FIG. 6 ;

FIG. 9 is a schematic diagram illustrating an example structure ofanother vibration sensor according to the third embodiment;

FIG. 10 is a diagram illustrating an example of an electric connectionof a sensor portion in the vibration sensor illustrated in FIG. 9 ;

FIG. 11 is a diagram illustrating an example of an electric connectionof a drive portion in the vibration sensor illustrated in FIG. 9 ;

FIG. 12A is a schematic diagram illustrating an example structure of avibration sensor according to a first example of a fourth embodiment;

FIG. 12B is a schematic diagram illustrating an example structure of avibration sensor according to a first example of a fourth embodiment;

FIG. 13A is a schematic diagram illustrating an example structure of avibration sensor according to a second example of the fourth embodiment;

FIG. 13B is a schematic diagram illustrating an example structure of avibration sensor according to a second example

FIG. 14 is a top view illustrating an example structure of a vibrationsensor according to a third example of the fourth embodiment;

FIG. 15 is a top view illustrating an example structure of a vibrationsensor according to a fourth example of the fourth embodiment;

FIG. 16 is a top view illustrating an example structure of a vibrationsensor according to a fifth example of the fourth embodiment;

FIG. 17 is a top view illustrating an example structure of a vibrationsensor according to a sixth example of the fourth embodiment;

FIG. 18A is a schematic diagram illustrating an example structure of avibration sensor according to a fifth embodiment;

FIG. 18B is a schematic diagram illustrating an example structure of avibration sensor according to a fifth embodiment;

FIG. 19A is a schematic diagram illustrating an example structure of avibration sensor according to a sixth embodiment;

FIG. 19B is a schematic diagram illustrating an example structure of avibration sensor according to a sixth embodiment;

FIG. 20 is a graph illustrating sensitivity characteristics with respectto the contraction ratio of the electrode in the length direction of thevibration sensor according to the sixth embodiment;

FIG. 21 is a graph illustrating sensitivity characteristics with respectto the contraction ratio of the electrode in the width direction of thevibration sensor according to the sixth embodiment;

FIG. 22 is a graph illustrating sensitivity characteristics in thevicinity of the resonance frequency of the vibration sensor in a case inwhich the shape and size of a common electrode are matched to the shapeand size of a sensing electrode in the sixth embodiment;

FIG. 23 is a graph illustrating sensitivity characteristics in thevicinity of the resonance frequency of the vibration sensor in a case inwhich the common electrode has a fixed size that is the same as the sizeof a piezoelectric layer in the sixth embodiment;

FIG. 24 is a schematic diagram illustrating an example structure ofanother vibration sensor according to the sixth embodiment;

FIG. 25 is a schematic diagram illustrating an example structure ofstill another vibration sensor according to the sixth embodiment;

FIG. 26 is a schematic diagram illustrating an example structure ofstill another vibration sensor according to the sixth embodiment;

FIG. 27 is a top view illustrating an example structure of a vibrationsensor according to a first example of a seventh embodiment;

FIG. 28 is a top view illustrating an example structure of a vibrationsensor according to a second example of the seventh embodiment;

FIG. 29 is a top view illustrating an example structure of a vibrationsensor according to a third example of the seventh embodiment;

FIG. 30 is a top view illustrating an example structure of a vibrationsensor according to a fourth example of the seventh embodiment;

FIG. 31 is a top view illustrating an example structure of a vibrationsensor according to a fifth example of the seventh embodiment;

FIG. 32 is a top view illustrating an example structure of a vibrationsensor according to a sixth example of the seventh embodiment; and

FIG. 33 is a block diagram illustrating an example structure of a sensormodule according to an eighth embodiment.

DETAILED DESCRIPTION

A vibration sensor according to an embodiment includes a laminated body.The laminated body includes a support layer a first end of which isfixed; a piezoelectric layer on the support layer; an insulating layerdisposed between the support layer and the piezoelectric layer; a commonelectrode disposed on a first principal surface of the piezoelectriclayer; a first sensing electrode disposed in a first area on a secondprincipal surface of the piezoelectric layer on the side opposite to thefirst principal surface; and a drive electrode disposed in a second areadifferent from the first area on the second principal surface of thepiezoelectric layer. The first area is located near the first end of thesupport layer.

Vibration sensors and a sensor module according to exemplary embodimentsare described in detail below with reference to the accompanyingdrawings.

Examples of vibration sensors include piezoresistive sensors thatutilize a piezoresistance effect, capacitive sensors that utilize achange in capacitance, and piezoelectric sensors that utilize apiezoelectric effect. Of the foregoing, piezoelectric vibration sensorsneed no external power supply, having a high degree of flexibility, andare also capable of generating enough power on their own to transmitdetected data by radio waves, having the advantage of consuming lesspower. Moreover, piezoelectric vibration sensors, in which excitationcan be achieved by applying a voltage, have an advantage in thatcalibration is possible not only for sensing but also for the sensorsthemselves.

Piezoelectric vibration sensors of micro electro mechanical systems(MEMS) are of great advantage to cost and size reductions. At the sametime, MEMS-type piezoelectric vibration sensors have difficulty inenhancing their sensitivity to minute vibrations and sometimes havedifficulty in achieving adequate sensitivity.

It is therefore an object of the embodiments described herein to providevibration sensors and a sensor module that are capable of enhancingtheir sensitivity to minute vibrations.

First Embodiment

A vibration sensor according to a first embodiment is first described indetail with reference to the drawings. FIG. 1A and FIG. 1B are schematicdiagrams illustrating an example structure of a vibration sensoraccording to the first embodiment. FIG. 1A is a top view of a vibrationsensor 10, and FIG. 1B is a sectional view taken along line A-A in FIG.1A.

As illustrated in FIG. 1A and FIG. 1B, the vibration sensor 10 accordingto the present embodiment is a MEMS-type piezoelectric vibration sensorincluding a cantilever structure (hereinafter referred to as acantilever structure for convenience of description), and includes asupport layer 101, an insulating layer 102, a common electrode 103, apiezoelectric layer 104, a sensing electrode 105, and a drive electrode106. The support layer 101, the insulating layer 102, the commonelectrode 103, the piezoelectric layer 104, the sensing electrode 105,and the drive electrode 106 constitute the cantilever structure juttingfrom a support 100.

The support layer 101 is a plate-like structure jutting from the support100. The support layer 101 may jut from the support 100 in such a mannerthat at least one principal surface is substantially normal to thesupport 100. The support layer 101 may be a member integral with thesupport 100, or may be a member different from that of the support 100.Various materials, such as bulk silicon, can be used as the material ofthe support layer 101. In the description, a principal surface is asurface that has the largest area in the structure. The support layer101 may be worked into a shape in which the weight concentrates on thetip of the cantilever structure, for example.

The plate-like support layer 101 includes two principal surfaces made upof the front and back sides thereof. Of these two principal surfaces,one principal surface (this is also referred to as a surface or topsurface) has the piezoelectric layer 104 arranged thereabove that hasthe same size as the principal surface, for example. Variouspiezoelectric materials, such as aluminum nitride (AlN), aluminumscandium nitride (AlScN), (K,Na) NbO₃ (KNN), zinc oxide (ZnO), leadzirconate titanate (PZT), lead zinc niobate (Pb(Zn_(1/3)Nb_(2/3))O₃:PZN-PT), lead magnesium niobate (Pb(Mg_(1/3)Nb_(2/3))O₃: PMN-PT), can beused for the piezoelectric layer 104.

Of two principal surfaces of the piezoelectric layer 104, one principalsurface on the support layer 101 side (this is referred to as a firstprincipal surface) has the common electrode 103 disposed thereon. Thecommon electrode 103 may have a size to cover the whole of the firstprincipal surface, or may have a size to cover a part of the firstprincipal surface. Metals, such as platinum (Pt), molybdenum (Mo),aluminum (Al), and gold (Au), or other conductive materials, forexample, can be used for the common electrode 103.

The insulating layer 102 is disposed between the common electrode 103and the support layer 101. This structure keeps the common electrode 103and the support layer 101 electrically separated. Various insulatingmaterials, such as silicon oxide (SiO₂), can be used for the insulatinglayer 102. The support layer 101 and the insulating layer 102 can becomposed of the same material (for example, an insulating material suchas silicon oxide).

Of the two principal surfaces of the piezoelectric layer 104, a secondprincipal surface on the side opposite to the first principal surfacehas the sensing electrode 105 and the drive electrode 106 disposedthereon. Metals, such as gold (Au), molybdenum (Mo), aluminum (Al), andplatinum (Pt), or other conductive materials, for example, can be usedfor the sensing electrode 105 and the drive electrode 106. The sensingelectrode 105 and the drive electrode 106 are both electrodes thatconfront the common electrode 103 through the piezoelectric layer 104.Of these electrodes, the sensing electrode 105 serves as an electrodefor extracting, as an electric signal, polarization generated on thesurface of the piezoelectric layer 104 by vibrations. Meanwhile, thedrive electrode 106 serves as an electrode for calibrating the vibrationsensor 10 by utilizing an inverse piezoelectric effect obtained byapplying an electric field to the piezoelectric layer 104.

The sensing electrode 105 and the drive electrode 106 are both designedto have optimum sizes and arrangements. For example, the sensingelectrode 105 may be disposed in an area that is on the second principalsurface of the piezoelectric layer 104 and near the base of thevibration sensor 10, which is a structure jutting from the support 100.Meanwhile, the drive electrode 106 may be disposed in the remaining areaon the second principal surface of the piezoelectric layer 104 so as tosurround the sensing electrode 105 (except the base side. the sameapplies hereinafter) while spacing a few micrometers to a few tens ofmicrometers from the sensing electrode 105.

When the vibration sensor 10 including the structure as described aboveundergoes a vibration from the outside, a stress is generated near thebase of the vibration sensor 10. As a result, an electric chargegenerated on the surface of the piezoelectric layer 104 by apiezoelectric effect builds up on the common electrode 103 and thesensing electrode 105 between which the piezoelectric layer 104 issandwiched. A potential difference arisen between the sensing electrode105 and the common electrode 103 is then detected, whereby the vibrationcan be detected.

With a structure in which resonance of the cantilever structure isutilized, the sensitivity to vibrations can be enhanced and frequenciesof the vibrations can also be identified depending on whether thestructure is in a resonance state.

Furthermore, in order to check the state of the vibration sensor 10itself, an alternating voltage can be applied to the drive electrode 106and the common electrode 103 to excite vibrations, thereby enablingcalibration to be performed. At that time, a potential differencebetween the sensing electrode 105 and the common electrode 103 isutilized to monitor the amplitude of the vibration sensor 10 duringcalibration, so that the state of the vibration sensor 10 itself can begrasped.

Because arranging the sensing electrode 105 near the base of thecantilever structure increases the output voltage of the vibrationsensor 10 during sensing, the sensitivity of the vibration sensor 10 tovibrations can be enhanced. Also, arranging the drive electrode 106 soas to surround the sensing electrode 105 can cause the vibration sensor10 to vibrate efficiently. As a result, driving performance and sensingsensitivity during calibration can be mutually compatible.

The size of the sensing electrode 105 is described next. In order todetermine the size of the sensing electrode 105, the dependence onsensitivity when the length and width of the sensing electrode 105 werechanged with respect to a length L and a width W of the second principalsurface of the piezoelectric layer 104 has been studied in the presentembodiment.

FIG. 2 is a diagram for illustrating the vibration sensor used for astudy to determine the size of a sensing electrode according to thepresent embodiment. As illustrated in FIG. 2 , the contraction ratio ofthe length of the sensing electrode 105 with respect to the length ofthe cantilever structure (corresponding to the length of the supportlayer 101) L is assumed to be Lc, the contraction ratio of the width ofthe sensing electrode 105 with respect to the width of the cantileverstructure (corresponding to the width of the support layer 101) W be Wc,the size of the piezoelectric layer 104 be the same as the size of thesupport layer 101, the length L of the piezoelectric layer 104 be 400μm, and the width W thereof be 50 μm in the study. The support layer 101is assumed to be a Si layer having a film thickness of 3 μm, theinsulating layer 102 be a SiO₂ layer having a film thickness of 200 nm,the common electrode 103 be a Pt layer having a film thickness of 100nm, the piezoelectric layer 104 be a PZT layer having a film thicknessof 3 μm, and the sensing electrode 105 be a Au layer having a filmthickness of 100 nm. Furthermore, as illustrated in FIG. 2 , the driveelectrode 106 is omitted, and the size of the common electrode 103 isassumed to be the same as the size of the first principal surface of thepiezoelectric layer 104 for convenience of description in the study.

FIG. 3 is a graph illustrating sensitivity characteristics with respectto the contraction ratio of the electrode in the length direction of thevibration sensor according to the present embodiment. FIG. 4 is a graphillustrating sensitivity characteristics with respect to the contractionratio of the electrode in the width direction of the vibration sensoraccording to the present embodiment. FIG. 3 and FIG. 4 illustratesensitivity characteristics as absolute values (corresponding to theoutput voltages) of the potential difference on the surfaces of upperand lower electrodes (corresponding to the common electrode 103 and thesensing electrode 105) with respect to the frequency of the vibration.

FIG. 3 illustrates the sensitivity characteristics when the contractionratio Lc of the sensing electrode 105 in the length direction is changedby 0.1 from 0.1 to 0.8 in a case in which the width of the sensingelectrode 105 is the same as the width W of the piezoelectric layer 104.As illustrated in FIG. 3 , when the contraction ratio Lc is 0.5, inother words, when the length of the sensing electrode 105 is half thelength L of the cantilever structure, the sensitivity characteristics ofthe vibration sensor 10 are most favorable. When the contraction ratioLc is within a range of 0.3 to 0.7, the sensitivity characteristics ofthe vibration sensor 10 are kept in a favorable range. Even when thecontraction ratio Lc is within a range of 0.1 to 0.3 or 0.7 to 0.9, itis evident that adequate sensitivity characteristics of the vibrationsensor 10 are achieved.

FIG. 4 illustrates the sensitivity characteristics when the contractionratio Wc of the sensing electrode 105 in the width direction is changedby 0.1 from 0.1 to 0.9 in a case in which the length of the sensingelectrode 105 is half the length L of the piezoelectric layer 104. Asillustrated in FIG. 4 , the sensitivity characteristics of the vibrationsensor 10 are stable toward the change of the sensing electrode 105 inthe width direction, compared with the sensitivity characteristics ofthe vibration sensor 10 toward the change of the sensing electrode 105in the length direction (see FIG. 3 ). When the contraction ratio Wc is0.5, in other words, when the width of the sensing electrode 105 is halfthe width W of the cantilever structure, the sensitivity characteristicsof the vibration sensor 10 are most favorable. When the contractionratio Wc is within a range of 0.3 to 0.7, the sensitivitycharacteristics of the vibration sensor 10 are kept in a favorablerange. Even when the contraction ratio Wc is within a range of 0.1 to0.3 or 0.7 to 0.9, it is evident that adequate sensitivitycharacteristics of the vibration sensor 10 are achieved. However, thesensing electrode 105 has lower limits of the length and width becauseof the constraints arising from its manufacturing process, the sensingelectrode 105 preferably has a length and width that are equal to orgreater than the lower length and width limits (for example, a fewmicrometers to 10 micrometers).

The findings suggest that the vibration sensor 10 has the highestsensitivity when both the width and the length of the sensing electrode105 are half the width W and the length L of the cantilever structure.

As described above, the vibration sensor 10 according to the presentembodiment is a MEMS-type piezoelectric vibration sensor including thecantilever structure, and includes the structure in which the sensingelectrode 105 is disposed near the base of the cantilever structure. Inthis manner, the sensing electrode 105 for detecting vibrations isdisposed near the base of the vibration sensor 10 on which the stressgenerated by vibrations concentrates, so that vibrations can be detectedmore effectively. Consequently, the sensitivity to vibrations can beenhanced.

The vibration sensor 10 according to the present embodiment can alsoutilize the resonance of the cantilever structure. Thus, the sensitivityto vibrations can be enhanced and frequencies of the vibrations can alsobe identified depending on whether the structure is in a resonancestate.

Furthermore, the drive electrode 106 is disposed in the entire remainingarea on the second principal surface of the piezoelectric layer 104 soas to surround the sensing electrode 105 while spacing a few micrometersto a few tens of micrometers from the sensing electrode 105 in thevibration sensor 10 according to the present embodiment. Consequently,the vibration sensor 10 can be achieved in which driving performance andsensing sensitivity are mutually compatible.

Second Embodiment

Subsequently, a vibration sensor according to a second embodiment isdescribed in detail with reference to the drawings. In the firstembodiment, the vibration sensor 10 has been described that has thecantilever structure in which one end is a fixed end and the other endis a free end. In contrast to this, a vibration sensor is described withan example that has a fixed-fixed beam structure in which both ends arefixed ends in the second embodiment. In the description below,components similar to those in the first embodiment are given the samereference numerals, and overlapping description thereof is omitted.

FIG. 5A and FIG. 5B are schematic diagrams illustrating an examplestructure of a vibration sensor according to the second embodiment. FIG.5A is a top view of a vibration sensor 20, and FIG. 5B is a sectionalview taken along line B-B in FIG. 5A.

As illustrated in FIG. 5A and FIG. 5B, the vibration sensor 20 accordingto the present embodiment includes a structure in which both ends of alaminated body that is made up of the support layer 101, the insulatinglayer 102, the common electrode 103, and the piezoelectric layer 104 arefixed to supports 100A and 100B in a structure similar to that of thevibration sensor 10 according to the first embodiment. A sensingelectrode 105A is disposed near the base of the laminated body on theside of the support 100A, and a sensing electrode 105B is disposed nearthe base of thereof on the side of the support 100B. In other words,stresses generated near the bases of two ends are utilized to sensevibrations in the vibration sensor 20 according to the presentembodiment. This enables vibrations to be detected more effectively, asis the case with the first embodiment. Consequently, the sensitivity tovibrations can be enhanced.

A drive electrode 206 may be disposed in the remaining area on thesecond principal surface of the piezoelectric layer 104 so as tosurround the sensing electrodes 105A and 105B while spacing a fewmicrometers to a few tens of micrometers from the sensing electrodes105A and 105B.

At least one of the supports 100A and 100B does not need to be a fixedmember, and may serve as a weight, for example. In this case, theamplitude of the output voltage from the vibration sensor 20 can beincreased, so that the sensitivity can be enhanced.

The vibration sensor 20 has a sectional structure and other structures,operations, and effects similar to those of the first embodiment, anddetailed description thereof is thus omitted.

Third Embodiment

Subsequently, a vibration sensor according to a third embodiment isdescribed in detail with reference to the drawings. In the presentembodiment, a case is described with an example in which a plurality ofvibration sensors according to embodiments described above or below areconnected to each other to constitute one vibration sensor. In thedescription below, components similar to those in the above embodimentsare given the same reference numerals, and overlapping descriptionthereof is omitted.

A case is first described in detail with reference to the drawings inwhich a plurality of vibration sensors 10 according to the firstembodiment are connected to each other to constitute one vibrationsensor. FIG. 6 is a schematic diagram illustrating an example structureof a vibration sensor according to the third embodiment. FIG. 7 is adiagram illustrating an example of an electric connection of a sensorportion in the vibration sensor illustrated in FIG. 6. FIG. 8 is adiagram illustrating an example of an electric connection of a driveportion in the vibration sensor illustrated in FIG. 6 .

As illustrated in FIG. 6 , a vibration sensor 30A having a cantileverstructure according to the present embodiment includes a structure inwhich a plurality of vibration sensors 10A to 10N each including astructure similar to the vibration sensor 10 according to the firstembodiment, for example, are arrayed. A plurality of vibration sensors10A to 10N may be fixed to the same support 100, or at least a partthereof may be fixed to a different support.

A sensor portion of the vibration sensor 30A having such a structureincludes a structure in which the sensing electrode 105 of a vibrationsensor 10 (for example, the vibration sensor 10A) is connected to thecommon electrode 103 of a vibration sensor 10 (for example, thevibration sensor 10B) that is arranged at the subsequent stage, asillustrated in FIG. 7 . In other words, if attention is focused on thesensor portion, a plurality of vibration sensors 10A to 10N areconnected in series. With this structure, the gain of the output voltagefrom the vibration sensor 30A can be increased in accordance with thenumber of vibration sensors 10 combined.

Meanwhile, a drive portion of the vibration sensor 30A includes astructure in which the drive electrodes 106 are connected in paralleland the common electrodes 103 are also connected in parallel across aplurality of vibration sensors 10A to 10N, as illustrated in FIG. 8 . Inother words, if attention is focused on the drive portion, a pluralityof vibration sensors 10A to 10N are connected in parallel. With thisstructure, a plurality of vibration sensors 10A to 10N can be driven bybatch during calibration, for example.

Subsequently, a case is described in detail with reference to thedrawings in which a plurality of vibration sensors 20 having thefixed-fixed beam structure according to the second embodiment areconnected to each other to constitute one vibration sensor. FIG. 9 is aschematic diagram illustrating an example structure of another vibrationsensor according to the third embodiment. FIG. 10 is a diagramillustrating an example of an electric connection of a sensor portion inthe vibration sensor illustrated in FIG. 9 . FIG. 11 is a diagramillustrating an example of an electric connection of a drive portion inthe vibration sensor illustrated in FIG. 9 .

As illustrated in FIG. 9 , a vibration sensor 30B having a cantileverstructure according to the present embodiment includes a structure inwhich a plurality of vibration sensors 20A to 20N each including astructure similar to the vibration sensor 20 according to the secondembodiment, for example, are arrayed. A plurality of vibration sensors20A to 20N may be fixed to the same supports 100A and 100B, or at leasta part thereof may be fixed to a different support.

As illustrated in FIG. 10 , a sensor portion of the vibration sensor 30Bincludes a structure in which a plurality of vibration sensors 20A to20N are connected in series, as is the case with the vibration sensor30A illustrated in FIG. 6 to FIG. 8 . With this structure, the gain ofthe output voltage from the vibration sensor 30B can be increasedaccording to the number of vibration sensors 20 combined. A series ofthe respective sensing electrode 105A sides of the vibration sensors 20Ato 20N connected in series and a series of the respective sensingelectrode 105B sides thereof connected in series may be independent fromeach other, or both series may be further connected to each other inseries. Alternatively, the respective sensing electrode 105A sides ofthe vibration sensors 20A to 20N and the respective sensing electrode105B sides thereof may be configured to be connected alternately inseries.

As illustrated in FIG. 11 , a drive portion of the vibration sensor 30Bincludes a structure in which a plurality of vibration sensors 20A to20N are connected in parallel, as is the case with the vibration sensor30A illustrated in FIG. 6 to FIG. 8 . With this structure, a pluralityof vibration sensors 20A to 20N can be driven by batch duringcalibration, for example.

As described above, the gain of the output voltage can be increased inaccordance with the number of vibration sensors 10 combined according tothe present embodiment. The vibration sensors 30A/30B can be achieved inwhich a plurality of vibration sensors can be driven by batch duringcalibration, for example.

The vibration sensors 10/20 each has a sectional structure and otherstructures, operations, and effects similar to those of the aboveembodiment, and detailed description thereof is thus omitted.

Fourth Embodiment

Subsequently, a vibration sensor according to a fourth embodiment isdescribed in detail with reference to the drawings. While the vibrationsensors 10/20 having the cantilever structure or the fixed-fixed beamstructure are illustrated by example in the above embodiments, vibrationsensors are described with examples that each include a structure inwhich a drive portion is shared across a plurality of vibration sensorsby tying respective one ends of the vibration sensors in a bundle in thepresent embodiment. In the description below, components similar tothose in the above embodiments are given the same reference numerals,and overlapping description thereof is omitted.

First Example

FIG. 12A and FIG. 12B are schematic diagrams illustrating an examplestructure of a vibration sensor according to a first example of thepresent embodiment. FIG. 12A is a top view of a vibration sensor 40A,and FIG. 12B is a sectional view taken along line C-C in FIG. 12A. Asillustrated in FIG. 12A and FIG. 12B, the vibration sensor 40A accordingto the first example includes a plurality of (four in the presentexample) sensor parts 41A to 41D that each have a cantilever structureand that are arranged at predetermined spacings, and a U-shaped drivepart 43A that binds the free end sides of the sensor parts 41A to 41D.In other words, the vibration sensor 40A according to the first exampleincludes a structure in which the drive portion (corresponding to thedrive part 43A) is shared across a plurality of vibration sensors eachhaving a cantilever structure, so that the respective tips of the sensorparts 41A to 41D are bound together.

The sensor parts 41A to 41D each include a structure in which a supportlayer 401, an insulating layer 402, a common electrode 403, apiezoelectric layer 404, and a sensing electrode 405 are laminated, asis the case with the sensor portions in the vibration sensors 10/20illustrated by example in the above embodiments, for example. In thefirst example, however, the sensing electrode 405 has the same width asthe width W of the piezoelectric layer 404. The drive part 43A alsoincludes a structure in which the support layer 401, the insulatinglayer 402, the common electrode 403, the piezoelectric layer 404, and adrive electrode 406 are laminated, as is the case with the driveportions in the vibration sensors 10/20.

In this manner, the structure in which the free end sides of the sensorparts 41A to 41D each having a cantilever structure are bound by thedrive part 43A can prevent sensitivity degradation of the sensor causedby drifts of the resonance frequencies of the sensor parts 41A to 41D.

Second Example

FIG. 13A and FIG. 13B are schematic diagrams illustrating an examplestructure of a vibration sensor according to a second example of thepresent embodiment. FIG. 13A is a top view of a vibration sensor 40B,and FIG. 13B is a sectional view taken along line D-D in FIG. 13A. Asillustrated in FIG. 13A and FIG. 13B, the vibration sensor 40B accordingto the second example includes a plurality of (four and four in thepresent example) sensor parts 41A to 41D and 41E to 41H that each have acantilever structure and that are arranged at predetermined spacings,and an H-shaped drive part 43B that binds the free end sides of thesensor parts 41A to 41D and 41E to 41H. A drive electrode 416 of thedrive part 43B is H-shaped. Of the sensor parts 41A to 41D and 41E to41H each having a cantilever structure, sensor parts facing each othersubstantially constitute a vibration sensor having a fixed-fixed beamstructure. The vibration sensor 40B according to the second exampletherefore includes a structure in which a drive portion (correspondingto the drive part 43B) is shared across a plurality of vibration sensorseach having a fixed-fixed beam structure, so that the respective tips ofthe sensor parts 41A to 41D and 41E to 41H are bound together.

The sensor parts 41A to 41D and 41E to 41H and the drive part 43B mayinclude a laminar structure similar to the structure of the sensor parts41A to 41D and the drive part 43A described above.

In this manner, the structure in which the drive part 43B is used as thecommon drive portion in the vibration sensor that has a fixed-fixed beamstructure and that is made up of the sensor parts 41A to 41D and 41E to41H, and the free end sides of the sensor parts 41A to 41D and 41E to41H are bound can prevent sensitivity degradation of the sensor causedby drifts of the resonance frequencies of the sensor parts 41A to 41Dand 41E to 41H, as is the case with the first example.

Third Example

FIG. 14 is a top view illustrating an example structure of a vibrationsensor according to a third example of the present embodiment. Asillustrated in FIG. 14 , a vibration sensor 40C according to the thirdexample includes a plurality of (four in the present example) sensorparts 41A to 41D, 41E to 41H, 41I to 41L, and 41M to 41P that each havea cantilever structure and that are arranged at predetermined spacings,and a rectangular drive part 43C that binds the free end sides of thesensor parts 41A to 41P. In other words, the vibration sensor 40Caccording to the third example includes a structure to hang therectangular drive part 43C located in the center so as to be surroundedby the sensor parts 41A to 41D, 41E to 41H, 41I to 41L, and 41M to 41P.The drive part 43C binds together the tips of the sensor parts 41A to41D, 41E to 41H, 41I to 41L, and 41M to 41P. The corner portions of therectangular drive part 43C are connected to support 100A to 100D. Therectangular corner portions of a drive electrode 426 extend to thesupport 100A to 100D.

The sensor parts 41A to 41P and the drive part 43C may include a laminarstructure similar to the structure of the sensor parts 41A to 41D andthe drive part 43A described above.

In this manner, a structure to hang the central rectangular drive part43C on every side with the sensor parts 41A to 41D, 41E to 41H, 41I to41L, and 41M to 41P having a cantilever structure enables the number ofsensor parts to be increased, so that the sensitivity of the vibrationsensor 40C can be further enhanced. The drive part 43C is not limited tobe rectangular, and may be changed into various shapes, such as acircle, oval, and a polygon with three or more sides.

Fourth Example, Fifth Example, and Sixth Example

FIG. 15 is a top view illustrating an example structure of a vibrationsensor according to a fourth example of the present embodiment. FIG. 16is a top view illustrating an example structure of a vibration sensoraccording to a fifth example of the present embodiment. FIG. 17 is a topview illustrating an example structure of a vibration sensor accordingto a sixth example of the present embodiment.

In a vibration sensor 40D according to the fourth example, which has astructure similar to the structure of the vibration sensor 40A accordingto the first example illustrated in FIG. 12A and FIG. 12B, therespective sensing electrodes 405 in the sensor parts 41A to 41D arereplaced with sensing electrodes 415, as illustrated in FIG. 15 .Likewise, in a vibration sensor 40E according to the fifth example,which has a structure similar to the structure of the vibration sensor40B according to the second example illustrated in FIG. 13A and FIG.13B, the respective sensing electrodes 405 in the sensor parts 41A to41D and 41E to 41H are replaced with the sensing electrodes 415, asillustrated in FIG. 16 . Likewise, in a vibration sensor 40F accordingto the sixth example, which has a structure similar to the structure ofthe vibration sensor 40C according to the third example illustrated inFIG. 14 , the respective sensing electrodes 405 in the sensor parts 41Ato 41P are replaced with the sensing electrodes 415, as illustrated inFIG. 17 . The sensing electrode 415 has a width reduced by thepredetermined contraction ratio Wc with respect to the width W of thepiezoelectric layer 404 as is the case with the first embodiment, forexample.

In this manner, the width of each sensing electrode 415 is optimized inthe fourth example, the fifth example, and the sixth example.Consequently, the sensitivity of the vibration sensors 40D, 40E, and 40Fcan be further enhanced.

Other structures, operations, and effects are similar to those of theabove embodiments, and detailed description thereof is thus omitted.

Fifth Embodiment

Subsequently, a vibration sensor according to a fifth embodiment isdescribed in detail with reference to the drawings. In the aboveembodiments, one of the sensing electrodes 105/405/415 constitutes onesensor portion in the vibration sensors. In contrast to this, a case isdescribed with an example in which the sensing electrodes 105/405/415 inthe sensor portions are each split into a plurality in the fifthembodiment. In the description below, components similar to those in theabove embodiments are given the same reference numerals, and overlappingdescription thereof is omitted. The description below is based on thevibration sensor 10 according to the first embodiment for convenience ofdescription, but not limited thereto. The same applies to the vibrationsensors according to the other embodiments.

FIGS. 18A and 18B are schematic diagrams illustrating an examplestructure of a vibration sensor according to the present embodiment.FIG. 18A is a top view of a vibration sensor 50, and FIG. 18B is asectional view taken along line E-E in FIG. 18A.

As illustrated in FIG. 18A, the vibration sensor 50 according to thepresent embodiment includes a structure in which the sensing electrode105 is replaced with a plurality of (three in the present example) splitelectrodes 105 a to 105 c, in a structure similar to the structure ofthe vibration sensor 10 according to the first embodiment.

A plurality of split electrodes 105 a to 105 c are electricallyconnected in series, for example. This enables vibrations to be detectedmore effectively. Consequently, the sensitivity to vibrations can beenhanced.

The vibration sensor 50 has a sectional structure and other structures,operations, and effects similar to those of the above embodiments, anddetailed description thereof is thus omitted.

Sixth Embodiment

Subsequently, a vibration sensor according to a sixth embodiment isdescribed in detail with reference to the drawings. In the aboveembodiments, the size and shape of the common electrode 103 are assumedto be the same as the size and shape of the first principal surface ofthe piezoelectric layer 104. In contrast to this, a case is described indetail with reference to the drawings in which the size and shape of thecommon electrode 103 are varied depending on the size and shape of thesensing electrode 105, for example, in the present embodiment. In thedescription below, components similar to those in the above embodimentsare given the same reference numerals, and overlapping descriptionthereof is omitted. The description below is based on the vibrationsensor 10 according to the first embodiment for convenience ofdescription, but not limited thereto. The same applies to the vibrationsensors according to the other embodiments.

FIGS. 19A and 19B are schematic diagrams illustrating an examplestructure of a vibration sensor according to the present embodiment.FIG. 19A is a top view of a vibration sensor 60A, and FIG. 19B is asectional view taken along line F-F in FIG. 19A.

As illustrated in FIGS. 19A and 19B, the vibration sensor 60A accordingto the present embodiment includes a structure in which the commonelectrode 103 is replaced with common electrodes 103 a and 103 b, in astructure similar to the structure of the vibration sensor 10 accordingto the first embodiment, for example. The common electrode 103 a has thesame size as the size of the sensing electrode 105, for example, and thecommon electrode 103 b has the same size as the size of the driveelectrode 106, for example.

As illustrated in FIGS. 19A and 19B, a trench 61 arising from a gapbetween the common electrodes 103 a and 103 b is present in apiezoelectric layer 604, depending on a manufacturing process duringwhich the vibration sensor 60A is manufactured.

The sizes of the sensing electrode 105 and the common electrode 103 aare described next. In the present embodiment, the common electrode 103a, which replaces the common electrode 103 in the vibration sensorillustrated with reference to FIG. 2 , has been used for a study todetermine the sizes of the sensing electrode 105 and the commonelectrode 103 a. Note that the material and the film thickness of thecommon electrode 103 a are the same as those of the common electrode103.

FIG. 20 is a graph illustrating sensitivity characteristics with respectto the contraction ratio of the electrode in the length direction of thevibration sensor according to the present embodiment. FIG. 21 is a graphillustrating sensitivity characteristics with respect to the contractionratio of the electrode in the width direction of the vibration sensoraccording to the present embodiment. FIG. 20 and FIG. 21 , as is thecase with FIG. 3 and FIG. 4 , illustrate sensitivity characteristics asabsolute values (corresponding to the output voltages) of the potentialdifference on the surfaces of upper and lower electrodes (correspondingto the common electrode 103 a and the sensing electrode 105) withrespect to the frequency of the vibration.

FIG. 20 illustrates the sensitivity characteristics when the contractionratio Lc of the sensing electrode 105 and the common electrode 103 a inthe length direction is changed from 0.05 to 0.9. As illustrated in FIG.20 , in a case in which the shape and size of the common electrode 103 aare matched to the shape and size of the sensing electrode 105, thesensitivity characteristics of the vibration sensor 60A are improvedwith decreased contraction ratio Lc, in other words, with decreasedratio with respect to the length L of the cantilever structure. Thesensitivity characteristics are most favorable when the contractionratio Lc is equal to or lower than 0.1. When the contraction ratio Lc isequal to or lower than 0.5, the sensitivity characteristics of thevibration sensor 60A are kept in a favorable range. When the contractionratio Lc is equal to or lower than 0.9, adequate sensitivitycharacteristics of the vibration sensor 60A are achieved.

FIG. 21 illustrates the sensitivity characteristics when the contractionratio Wc of the sensing electrode 105 and the common electrode 103 a inthe width direction is changed by 0.1 from 0.1 to 0.9. As illustrated inFIG. 21 , the sensitivity characteristics of the vibration sensor 60Aare stable toward the change of the sensing electrode 105 and the commonelectrode 103 a in the width direction, although the sensitivitycharacteristics of the vibration sensor 60A are most favorable when thecontraction ratio Wc is 0.5. When the contraction ratio Wc is within arange of 0.3 to 0.7, the sensitivity characteristics of the vibrationsensor 60A are kept in a favorable range. Even when the contractionratio Wc is within a range of 0.1 to 0.3 or 0.7 to 0.9, it is evidentthat adequate sensitivity characteristics of the vibration sensor 60Aare achieved.

However, the sensing electrode 105 and the common electrode 103 a havelower limits of the length and width because of the constraints arisingfrom their manufacturing process, the sensing electrode 105 and thecommon electrode 103 a preferably have lengths and widths that are equalto or greater than the lower length and width limits (for example, a fewmicrometers to 10 micrometers).

A description is now given of which of the following two cases obtainsbetter sensitivity characteristics: a case in which the common electrode103 has a fixed size that is the same as the size of the piezoelectriclayer 104 (for example, the first embodiment); and a case in which theshape and size of the common electrode 103 a are matched to the shapeand size of the sensing electrode 105 (for example, the presentembodiment). In the description, the length and the width of the sensingelectrode 105 are assumed to be half the length L and the width W of thepiezoelectric layer 104, in other words, the contraction ratios Lc andWc are both assumed to be 0.5.

FIG. 22 illustrates sensitivity characteristics in the vicinity of theresonance frequency of the vibration sensor in a case in which the shapeand size of the common electrode are matched to the shape and size ofthe sensing electrode. FIG. 23 illustrates sensitivity characteristicsin the vicinity of the resonance frequency of the vibration sensor in acase in which the common electrode has a fixed size that is the same asthe size of the piezoelectric layer. FIG. 22 and FIG. 23 , as is thecase with FIG. 20 and FIG. 21 , illustrate sensitivity characteristicsas absolute values (corresponding to the output voltages) of thepotential difference on the surfaces of upper and lower electrodes(corresponding to the common electrodes 103/103 a and the sensingelectrodes 105) with respect to the frequency of the vibration.

As is evident from comparison between FIG. 22 and FIG. 23 , the outputvoltage of the vibration sensor is increased more in the case in whichthe shape and size of the common electrode 103 a are matched to theshape and size of the sensing electrode 105 (for example, the presentembodiment) than the case in which the common electrode 103 has a fixedsize that is the same as the size of the piezoelectric layer (forexample, the first embodiment). This shows that the sensitivitycharacteristics are enhanced more with the vibration sensor having astructure in which the shape and size of the common electrode 103 a arematched to the shape and size of the sensing electrode 105 (for example,the vibration sensor 60A) than the vibration sensor having a structurein which the common electrode 103 has a fixed size that is the same asthe size of the piezoelectric layer (for example, the vibration sensor10).

Thus, optimizing the sizes of the sensing electrode 105 and the commonelectrode 103 a can further improve the output voltage, thereby furtherenhancing the sensitivity to vibrations.

The findings as described above are not limited to the vibration sensor60A based on the vibration sensor 10 having the cantilever structureaccording to the first embodiment. The same can apply to a vibrationsensor 60B, as illustrated in FIG. 24 , for example, based on thevibration sensor 20 having the fixed-fixed beam structure according tothe second embodiment. In the vibration sensor 60B illustrated in FIG.24 , the common electrode 103 is split into a common electrode 103Acorresponding to the sensing electrode 105A, a common electrode 103Bcorresponding to the sensing electrode 105B, and a common electrode 103Ccorresponding to a drive electrode 216. Trenches 61A and 61B arisingfrom gaps between the common electrodes 103A to 103C are present in apiezoelectric layer 614.

Although FIG. 19A, FIG. 19B, and FIG. 24 illustrate by example the casesin which the common electrode 103 is separated to conform to the shapesof the sensing electrodes 105/105A/105B and the drive electrodes106/216, the vibration sensors are not limited to these structures.Structures can be such that, in addition to the common electrode 103,the piezoelectric layer 104 is also separated to conform to the shapesof the sensing electrodes 105/105A/105B and the drive electrodes106/216, as illustrated in FIG. 25 and FIG. 26 , for example.

A vibration sensor 60C illustrated in FIG. 25 is based on the vibrationsensor 10 according to the first embodiment, for example, and includes astructure in which the piezoelectric layer 604 is replaced withpiezoelectric layers 604 a and 604 b, in a structure similar to thestructure of the vibration sensor 60A illustrated in FIG. 19A and FIG.19B, for example. The piezoelectric layers 604 a has the same size asthe size of the sensing electrode 105, for example, and thepiezoelectric layers 604 b has the same size as the size of the driveelectrode 106, for example. A trench 62, on the underside thereof,exposes the insulating layer 102.

A vibration sensor 60D illustrated in FIG. 26 is based on the vibrationsensor 20 according to the second embodiment, for example, and includesa structure in which the piezoelectric layer 614 is replaced withpiezoelectric layers 614A, 614B, and 614C, in a structure similar to thestructure of the vibration sensor 60B illustrated in FIG. 24 , forexample. The piezoelectric layers 614A has the same size as the size ofthe sensing electrode 105A, for example, the piezoelectric layers 614Bhas the same size as the size of the sensing electrode 105B, forexample, and the piezoelectric layers 614C has the same size as the sizeof the drive electrode 216, for example. Trenches 62A and 62B, on theunderside thereof, expose the insulating layer 102.

Each of the vibration sensors 60A, 60B, 60C, and 60D0 has a sectionalstructure and other structures, operations, and effects similar to thoseof the above embodiments, and detailed description thereof is thusomitted.

Seventh Embodiment

Subsequently, a vibration sensor according to a seventh embodiment isdescribed in detail with reference to the drawings. In the thirdembodiment described above, the vibration sensors 10/20 both having thesame length L are arrayed and electrically connected. In contrast tothis, a case is described with an example in which vibration sensorshaving a length L different from each other are arrayed and electricallyconnected in the present embodiment. In the description below,components similar to those in the above embodiments are given the samereference numerals, and overlapping description thereof is omitted.

First Example

FIG. 27 is a top view illustrating an example structure of a vibrationsensor according to a first example. As illustrated in FIG. 27 , avibration sensor 70A according to the first example includes one each ofvibration sensors 71A to 71N having a cantilever structure and having alength L different from each other. The vibration sensors 71A to 71N maybe fixed to the same support 100, or at least a part thereof may befixed to a different support. The exemplary electric connection of thesensor part and the drive part as well as the sectional structure of thevibration sensors 71A to 71N may be the same as those of any of thevibration sensors having a cantilever structure in the aboveembodiments, for example.

Second Example

FIG. 28 is a top view illustrating an example structure of a vibrationsensor according to a second example. As illustrated in FIG. 28 , avibration sensor 70B according to the second example includes aplurality of each (two each in the present example) of vibration sensors71A to 71N each having the same length L, in a structure similar to thestructure of the vibration sensor 70A according to the first example.

Third Example

FIG. 29 is a top view illustrating an example structure of a vibrationsensor according to a third example. As illustrated in FIG. 29 , avibration sensor 70C according to the third example has a structure inwhich the respective free end sides of the vibration sensors 71A to 71Nare fixed to supports 100B1 to 100Bn, in a structure similar to thestructure of the vibration sensor 70A according to the first example.The supports 100B1 to 100Bn may be one support, or a support split intoa plurality.

Fourth Example

FIG. 30 is a top view illustrating an example structure of a vibrationsensor according to a fourth example. As illustrated in FIG. 30 , avibration sensor 70D according to the fourth example has a structure inwhich the respective free end sides of the vibration sensors 71A to 71Neach having the same length L are fixed to respective common supports100B1 to 100Bn, in a structure similar to the structure of the vibrationsensor 70B according to the second example. The supports 100B1 to 100Bnmay be one support, or a support split into a plurality.

Fifth Example

FIG. 31 is a top view illustrating an example structure of a vibrationsensor according to a fifth example. As illustrated in FIG. 31 , avibration sensor 70E according to the fifth example has a structure inwhich the vibration sensors 71A to 71N having a cantilever structure andhaving a length L different from each other is replaced with vibrationsensors 72A to 72N having a fixed-fixed beam structure and having alength L different from each other, in a structure similar to thestructure of the vibration sensor 70C according to the third example.The exemplary electric connection of the sensor part and the drive partas well as the sectional structure of the vibration sensors 72A to 72Nmay be the same as those of any of the vibration sensors having afixed-fixed beam structure in the above embodiments, for example.

Sixth Example

FIG. 32 is a top view illustrating an example structure of a vibrationsensor according to a sixth example. As illustrated in FIG. 32 , avibration sensor 70F according to the sixth example includes a pluralityof each (two each in the present example) of vibration sensors 72A to72N each having the same length L, in a structure similar to thestructure of the vibration sensor 70E according to the fifth example.

The vibration sensors 71A to 71N and 72A to 72N each have a resonancefrequency in accordance with the length L. As a result, the sensing bandcan be widened by arraying a plurality of vibration sensors having alength L different from each other, as in the first to the sixthexamples.

At that time, the gain of the output voltage when vibrations at eachresonance frequency is detected can be increased in accordance with thenumber of vibration sensors combined, by disposing a plurality ofvibration sensors having the same length L, as in the second, thefourth, and the sixth examples.

Other structures, operations, and effects are similar to those of theabove embodiments, and detailed description thereof is thus omitted.

Eighth Embodiment

Subsequently, a sensor module according to an eighth embodiment isdescribed in detail with reference to the drawing. In the eighthembodiment, the sensor module is described with an example that includesthe vibration sensors according to the above embodiments. In thedescription below, components similar to those in the above embodimentsare given the same reference numerals, and overlapping descriptionthereof is omitted. A case in which the vibration sensor 10 according tothe first embodiment is used is described below for convenience ofdescription, but the vibration sensor to be used is not limited thereto.The vibration sensors according to the other embodiments can also beused.

FIG. 33 is a schematic diagram illustrating an example structure of thesensor module according to the present embodiment. As illustrated inFIG. 33 , a sensor module 80 includes a controller 81 and a memory 82,in addition to the vibration sensor 10.

The controller 81 is made up of an information-processing device, suchas a central processing unit (CPU), and detects vibrations input to thevibration sensor 10 on the basis of the potential difference arisenbetween the sensing electrode 105 and the common electrode 103. Thecontroller 81 applies a voltage signal of the frequency corresponding tothe resonance frequency of the vibration sensor 10 to the driveelectrode 106 and the common electrode 103 during calibration of thevibration sensor 10, for example.

The memory 82 is a storage device, such as a dynamic random accessmemory (DRAM), and stores various computer programs and parameters toenable the operation of the controller 81 and data on vibrationsdetected by the vibration sensor 10. Various computer programs andparameters include computer programs and parameters to be used forcalibration of the vibration sensor 10.

Other structures, operations, and effects are similar to those of theabove embodiments, and detailed description thereof is thus omitted.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A vibration sensor comprising a plurality oflaminated bodies including a first laminated body and a second laminatedbody, each of the plurality of laminated bodies including: support layera first end of which is fixed; a piezoelectric layer on the supportlayer; an insulating layer disposed between the support layer and thepiezoelectric layer; a common electrode disposed on a first principalsurface of the piezoelectric layer; a first sensing electrode disposedin a first area on a second principal surface of the piezoelectric layeron a side opposite to the first principal surface; and a drive electrodedisposed in a second area different from the first area on the secondprincipal surface of the piezoelectric layer, wherein the first area islocated near the first end of the support layer, the first sensingelectrode in the first laminated body is electrically connected to thecommon electrode in the second laminated body, and the drive electrodein the first laminated body is electrically connected to the driveelectrode in the second laminated body.
 2. The vibration sensoraccording to claim 1, wherein the second area is an area that surroundsthe first area from sides other than the first end while being spacedfrom the first area.
 3. The vibration sensor according to claim 1,further comprising a second sensing electrode disposed in a third areaon the second principal surface of the piezoelectric layer, wherein asecond end, which is different from the first end, of the support layeris fixed, in addition to the first end, and the third area is locatednear the second end of the support layer.
 4. The vibration sensoraccording to claim 1, wherein the respective support layers of thelaminated bodies each include a common portion shared with other supportlayers on a side of a second end different from the first end, and therespective drive electrodes of the laminated bodies are located on thecommon portion of the support layers.
 5. The vibration sensor accordingto claim 4, wherein the second laminated body is located on a sideopposite to the first laminated body from the common portion.
 6. Thevibration sensor according to claim 4, wherein the laminated bodies areconnected to the common portion so as to surround the common portion. 7.The vibration sensor according to claim 1, wherein the common electrodeincludes: a first electrode having a surface that faces the firstsensing electrode, the surface having a shape identical to a shape ofthe first sensing electrode, the first electrode being disposed at aposition confronting the first sensing electrode through thepiezoelectric layer; and a second electrode having a surface that facesthe drive electrode, the surface having a shape identical to a shape ofthe drive electrode, the second electrode being disposed at a positionconfronting the drive electrode through the piezoelectric layer.
 8. Thevibration sensor according to claim 7, wherein the piezoelectric layerincludes: a first layer having a surface that is in contact with thefirst sensing electrode, the surface having a shape identical to a shapeof the first sensing electrode; and a second layer having a surface thatis in contact with the drive electrode, the surface having a shapeidentical to a shape of the drive electrode.
 9. The vibration sensoraccording to claim 7, wherein the piezoelectric layer has a surface thatfaces the support layer, the surface having a shape identical to a shapeof the support layer.
 10. The vibration sensor according to claim 7,wherein the first sensing electrode has a length beginning at a side ofthe first end that is equal to or smaller than 0.1 times a length of thesupport layer beginning at the first end.
 11. The vibration sensoraccording to claim 7, wherein the first sensing electrode has a lengthbeginning at a side of the first end that is equal to or smaller than0.5 times a length of the support layer beginning at the first end. 12.The vibration sensor according to claim 1, wherein each of the laminatedbodies has a length beginning at the first end that is different fromlengths of other laminated bodies beginning at the first end.
 13. Thevibration sensor according to claim 1, wherein at least one of thelaminated bodies has a length beginning at the first end that isdifferent from lengths of other laminated bodies beginning at the firstend.
 14. The vibration sensor according to claim 1, wherein the supportlayer and the insulating layer are composed of a same material.
 15. Thevibration sensor according to claim 1, wherein the first sensingelectrode includes a plurality of split electrodes formed in a separatedarea of the first area on the second principal surface.
 16. Thevibration sensor according to claim 15, wherein the split electrodes areelectrically connected in series.
 17. The vibration sensor according toclaim 1, wherein the first sensing electrode has a length beginning at aside of the first end that is half a length of the support layerbeginning at the first end.
 18. The vibration sensor according to claim1, wherein the first sensing electrode has a length beginning at a sideof the first end that is between or equal to 0.3 times and 0.7 times alength of the support layer beginning at the first end.
 19. A sensormodule comprising: the vibration sensor according to claim 1; and acontroller connected to the vibration sensor, the controller configuredto detect vibrations input to the vibration sensor, based on a potentialdifference arisen between the first sensing electrode and the commonelectrode, and to excite the vibration sensor by applying a voltagesignal of a predetermined frequency to the drive electrode and thecommon electrode.